Thick film pastes are compositions comprising inorganic particles, such as metals and metal oxides, dispersed in an organic medium. Among the metals commonly used are lead and cadmium. Solvents such as terpenes, kerosene, dibutylphthalate, butyl carbitol, butyl carbitol acetate, hexylene glycol, high boiling alcohols and alcohol esters are typically included in the organic medium. Finely divided particles of inorganic binder and other additives may also be included. These paste compositions are used to make electrical circuits and devices such as resistors and capacitors.
The packaging and transportation of thick film pastes has been problematic for years. Many thick film pastes are toxic to humans. For this and other reasons, various governmental agencies have imposed labelling requirements on thick film paste containers. However, thick film pastes commonly are sold in quantities as small as one ounce, two ounces and four ounces. The containers for such small quantities are too small to legibly display all the required label information. Including the information as a package insert is unacceptable because the information can be separated from the paste. Packaging the small quantities of paste in containers large enough to legibly display all of the information has been unsatisfactory also. Organic medium tends to evaporate from the paste in the oversized containers and removal of the paste from these containers is difficult.
The toxicity of thick film pastes renders removal of the paste from the container important to the packaging and transportation of the paste. Containers like paint cans and baby food jars have been used for thick film pastes. These containers do not allow the paste to be removed completely without requiring a special tool to reach all of the paste or requiring a person to put his or her hand dangerously close to the paste.
In addition to considerations regarding toxicity, many thick film pastes are frequently classified as flammable material. To transport these materials commercially, the paste containers must be substantially impermeable with respect to the paste, and capable of withstanding pressure differentials typically experienced during transport, especially transport by air, drops from prescribed heights and having prescribed weights stacked thereon. The glass jars commonly used are fragile and easily broken during transportation. To survive commercial transport intact, glass jars are specially packed in shock absorbent materials. Despite such special packing, the lids on these jars have been known to be dislodged by the pressure differentials experienced during transport by air. The paint can containers which have been used are difficult to grasp and handle, especially when trying to remove the lid, have been dented and crushed during commercial transport and have had the lid dislodged under commercial transport pressure differentials. Conventional polypropylene wide-mouth jars having standard screw thread lids and relatively square corners have also been used as containers for thick film pastes. However, under the pressure differentials experienced during air transport, the polypropylene walls tend to deform and the screw threads on the jar have been known to pull away from the screw threads on the lid, thereby dislodging the lid from the polypropylene jar.